Hi Hariharan, which silane derivative do you mean? SiMe3 or SiH3 or any other?

Hi Hariharan,

If I've well understood, you have a Si-O-Si (siloxane bond) between your compound and the silica, right?

Hi Hariharan,

standard procedure for the cleavage of the Si-O- bond in organic silicon ethers is with fluoride salts (tetraalkylammonium fluoride in tetrahydrofurane etc.). But the Formation of the weak acid HF could destroy your silica backbone. This might be avoided by the use of diluted aqueous or alcoholic solutions of fluorides under neutral or weakly basic conditions.

anyway, these are articles dealing with comparable topics:

Cleavage of Si-O bonds:

Cleavage of the SiO- Si(CH3) 2H bond in Si8O20[Si(CH3) 2H] 8, Hasegawa, Isao; Imamura, Wataru; Takayama, Toshio, Inorganic Chemistry Communications (2004), 7(4), 513-515.

Cleavage of the Si-C bonds:

Oxidative Cleavage of Carbon- Silicon Bond as a New Method To Characterize Bonded Stationary Phases on Silica Gel, Yang, Anle; Li, Tingyu, Analytical Chemistry (1998), 70(14), 2827-2830.

Dear all,  I use Aminosilane (3-Aminopropyl)triethoxysilane (APTES)) to functionalize silica fiber surface with antibodes (biosensors). After using the fiber probes in my experiments I want to reuse them. For this I am looking for a solvent that would cleave APTES for the surface and regenerate silanol groups. @Boege, I think fluoride solutions might work for this particular application. Will Piranha (H2O2 + Sulfuric acid) or Sulphochromic acid be useful to break- Si-O-APTES bonds?

Hi Hariharan,

I'm also working with trialkoxysilane (GPTMS and GPTES).

If the antibodies you use are stable in water at basic pH (around 12), you could retrieve them by breaking the Si-O-Si bond at this pH. Your functionalized antibodies would then be under silanolates form. After that, you would have to find a way to separate it from the silica (filtration, dialysis,...).

But be aware that when you will neutralize the media, new siloxane bond will be formed as silanol are quickly condensating on each other to give Si-O-Si bonds.

About the piranha solution, in my opinion, you will completely destroy your antibodies as it is one of the strongest acid available in classic lab.

Best regards

@Guillory, I my experiments I need to recover the bare silica fiber probe with silanol bonds (meaning: I need to remove both Silane and the attached antibodies). Currently  I am using piranha solution but I think silane is not completely removed.

Hi Hariharan,

Sorry I misunderstood what you wanted to revover ! I thought you wanted to reuse the antibodes and not the silica fibers.

Then the piranha is probably a good way to "burn off" the antibodies, but tour questionning is legitimate, there could be remaining APTES fragment on the surface.

If you have access to a 29Si MAS NMR you check it out by verifying is any T species exist. You shloud only have Q species if the piranha works well.

Otherwide, try the fluoride salts (TBAF,..) recommended by Matthias Boege. But then maybe be careful to not introduce fluoride ion on your fibers. I don't know much about the use of TBAF on bare silica. I'm more used to small organic components.

Good luck in your research, Best regards.

Exactly Guillory, Fluorides would damage the probe. I will try strong acids. Thank you very much :)

Hi Hariharan,

Xaviers idea of using 29Si MAS NMR is a very good one! you could also check the remaining organic content of your rinsed samples by elemental analysis. If you just want to remove the organic stuff from the surface of your silica particles I think it's indeed best to do it on an acid and oxidizing way as you intended - have you tried hot concentrated HNO3 for this purpose, yet?

Best regards and good luck

@Kampfe I havn't used Conc. HNO3 yet. I was previously using H2O2+H2SO4 or H2CrO4 (sulphochromic acid). I am sure that these strong acids can remove organic compound which adhere on the glass substrate, my doubt is whether these acids are good for removing covalently bound silane molecules for the glass surfaces.

Hi Hariharan, your right, I'm also sure that the acids you already used remove most of the organic stuff. In case of sulphochromic acid I'd be afraid that there will remain some Cr in your particles what might be disadvantageous for your further chemistry. Hot and concentrate nitric acid will also attack the organic part of a trimethylsilyl group, leaving behind a "new born" trihydroxysilyl group. However, I guess this group is what you might look for in terms of resilylation. The only thing is that while applying this method your particle grows by a two atom layer each cycle. But this is the case for the acids you mentioned, too. Any traces of HNO3 may afterwards be removed more easily, as HNO3 is less viscous and more volatile than H2SO4 and contains no Cr.  Have fun with silicon chemistry! Best Regards

As Alexander stated all of the mentioned oxidising media will remove the organyl part of the silane the silicon is covalently bonded. Only HF will remove each the Si-surface which I would not suggest. But keep in mind that the molecule is not removed (it will be fragmented). You can also use temperature (furnace or burning) or UV-irradiation.

THanks Kampfe :)

@Schmitt, Currently, I introduce the silane bound silica surface to butane flame. In this process the covalently bound silane is oxidized.

@ Hariharan How did you remove the APTES finally ? 

I want to remove Triethylsilane (TES) from Quartz surface using acetone and followed by nitric acid wash but it is not removed. Can any person help?

Dr. Sujoy Biswas Try out Piranha solutions which are generally used to remove organic residues from substrates. Usually, piranha solution is a 3:1 mixture of sulfuric acid and 30% hydrogen peroxide.

Caution: Piranha is corrosive. Reference: https://ehs.princeton.edu/book/export/html/513

Thanks

Hariharan Manoharan were you able to successfully remove the silane layer from the silica surface? Could you please share your experience? Thanks.